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Vectors help!

I'm working through the Solomon Worksheets for vectors and the question is to "find in degrees to 1dp, the angle made with the vector 'i' by the vector..."
I'm on 'd' and my answer is apparently wrong, I've been correct for all others. Where did I go wrong?
image.jpg
Reply 1
looks like it wanted the obtuse angle not the acute angle. I can't really see from your tiny working and upside down screenshot, you haven't finished typing up the question, I don't know what goes after the '...' i'd need more info
(edited 7 years ago)
Original post by Sayless
looks like it wanted the obtuse angle not the acute angle. I can't really see from your tiny working and upside down screenshot, you haven't finished typing up the question, I don't know what goes after the '...' i'd need more info


You can click the picture to expand it..
Reply 3
Original post by mnaj123
I'm working through the Solomon Worksheets for vectors and the question is to "find in degrees to 1dp, the angle made with the vector 'i' by the vector..."
I'm on 'd' and my answer is apparently wrong, I've been correct for all others. Where did I go wrong?
image.jpg


You've drawn your i\mathbf{i} vector the wrong way around. I would highly recommend always overlaying axes, then drawing your vectors.



You need the angle in green, since you want the direction with the i vector, which points rightwards. Had it asked you for the angle with the x-axis, then it would have been okay to give the red angle. But the question is asking for the angle between the i vector which is the black line pointing rightwards and the blue line pointing top-left. Hence you need the angle in green.

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